Color images are well known to be formed by reacting couplers with oxidized color developing agents of the primary amine type, which have been oxidized using optically exposed silver halides as an oxidizing agent, to produce indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine and their analogous dyes.
In order to form magenta color images, couplers of 5-pyrazolone, cyanoacetophenone, indazolone, pyrazolobenzimidazole and pyrazolotriazole types have been employed.
Most of the magenta color image-forming couplers which have been studied and widely used up to the present are 5-pyrazolones. However, dyes produced from 5-pyrazolone type couplers show an undesired absorption having a yellow component in the neighborhood of 430 nm, which is responsible for color turbidity.
As nuclei of magenta color image-forming couplers which reduce the aforesaid yellow component, there have been proposed pyrazolobenzimidazole nuclei in British Patent No. 1,047,612, indazolone nuclei in U.S. Pat. No. 3,770,447, and pyrazolo[5,1-c]-1,2,4-triazole nuclei in U.S. Pat. No. 3,725,067.
However, magenta couplers disclosed in the above-cited patents remain unsatisfactory. For instance, when these couplers are mixed with a silver halide emulsion dispersed in a hydrophilic protective colloid like gelatin, color images produced therefrom are unsatisfactory; their solubilities in high boiling organic solvents are low; they are difficult to synthesize; they have no more than comparatively low coupling activities in ordinary developers; and dyes produced therefrom have extremely low fastness to light.
As a result of searching for magenta couplers without subsidiary absorption in the neighborhood of 430 nm, which is the most serious defect of 5-pyrazolone type couplers in respect of hue, the present inventors found that 1H-pyrazolo[1,5-b]-1,2,4-triazole type magenta couplers showed no subsidiary absorption in the short wavelength region, produced color images of high fastness and were synthesized with ease, and disclosed them in JP-A-No. 59-171956 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and U.S. Pat. No. 4,540,654. These couplers further have advantages in that they are excellent in color reproducibility and synthesizing facility, and can be converted to two-equivalent couplers by introducing a splitting-off group to the coupling active site, to reduce the amount of silver to be used.
However, these couplers had low color developability, and the photographic properties of the magenta images produced therefrom were greatly changed with fluctuation in concentrations of ingredients contained in processing baths (e.g., sulfite ion and a hydroxylamine derivative added to a developer as an oxidation inhibitor for a color developing agent) under running processing.
As a means for overcoming these defects, introduction of an alkyloxy group or an aryloxy group in the 6-position of the foregoing 1H-pyrazolo[1,5-b]-1,2,4-triazole type magenta couplers has been disclosed in JP-A-No. 62-209457. Though successful in enhancing color developability and considerably depressing the changes in photographic properties under running processing, this coupler had a problem of the generation of stain (increase in density of unexposed areas) with the lapse of time after photographic processing.
Stains caused in a silver halide color photographic material are undesirable, since they not only degrade the quality of white areas of the image but also aggravate the turbidity in colored areas of the image and spoil the visual sharpness of the image. In particular, the reflection density of stains in reflex materials (e.g., color paper) is, in theory, emphasized several times over the transmission density. Therefore, only slight stains spoil the image quality and result in a serious problem. Although the incorporation of the compounds described in JP-A-No. 62-96944 and JP-A-No. 62-92945 into sensitive materials was disclosed for the purpose of suppressing the generation of stains, those compounds still cannot produce sufficient effects upon the couplers in question.
On the other hand, the art of using hindered amines and pyrazolotriazole type couplers in combination is disclosed in European Patent No. 218,266. However, the patent does not have any examples in which the pyrazolotriazole type couplers substituted by an alkyloxy group, an aryloxy group or a heterocyclyl group at the 6-position are used. Therefore, it is not easy to analogize the effects of the present invention from the above-cited patent.
Under these circumstances, a new method of lessening the influences of fluctuation in processing conditions and depressing the increase of stain is greatly desired.